1. Field of the Invention
The present invention relates to an improved, safe and reliable method of separating a superalloy metal powder from contaminants, such as process-produced contaminants.
2. Description of the Prior Art
It has been known in connection with powder metal product manufacture to monitor and separate contaminants therefrom in order to produce higher quality products from the metal powder. It has also been known to employ quality assurance methods wherein it is desired to detect and characterize process-produced contaminants for superalloy metal powders as a means for enhancing the quality of product made therefrom particularly in products wherein the consequences of failure are particularly serious.
It has been known to detect and characterize the concentration of process-produced contaminants by first concentrating the processed-produced contaminants by heavy liquid separation processes, such as those employing thallium malonate formate, into an aliquot which was subsequently examined by microscopy methods. This process separates the metal powder which may have a density of about 8.0 grams/cm2 from oxides which may have a density of about 4.0 grams/cm2 or less as a result of the density differences. It is also desired in such processes to increase the volume of the processed powder metal sample in order to improve the statistical reliability of the microscopy methods.
A serious problem with the use of thallium malonate formate is that it is potentially hazardous. It requires the services of specially trained technicians as well as continuous monitoring of the technicians' exposure levels, special laboratory handling equipment and special disposal methods. Further, it has a limited batch size which may be about ¼ pound, and a process time of about one batch per eight-hour shift, for example. The small batch size limits the accuracy of the quality assurance analysis for detecting process-produced contaminant particles. Further, these negative factors contribute directly or indirectly to increased overall costs of the quality assurance process.
It has been suggested to employ two-stage oxidation of the surface of metal particles which consists mainly of iron and an oxidation environment at an elevated temperature in order to enhance stability of the metal particles. See, for example, U.S. Pat. No. 4,318,735. See also U.S. Pat. No. 4,608,093 which discloses gradual oxidation of ferromagnetic particles in order to create a stable oxide coating that will resist deterioration under the influence of temperature and humidity. The heating is said to occur in two stages at temperatures up to 150° C.
U.S. Pat. No. 4,909,865 discloses a ferromagnetic metal powder composed mainly of iron which is provided with an oxide coating for uses in magnetic recording media.
U.S. Pat. No. 5,062,904 discloses the processing of ferromagnetic particles which are said to be provided with enhanced storage stability through oxidation of the surface under the influence of plasma in an oxygen atmosphere.
U.S. patent Publication No. 2002/0144753 discloses a method of producing a rare earth metal-based permanent magnet having a thin film layer through placing the rare earth permanent magnet and a fine metal powder forming material into a treating vessel and vibrating them and agitating them.
U.S. Pat. No. 3,516,612 discloses the resistance to forming of clumps or aggregates in fine particles for a magnetic material due to a combination of an imposed magnetic field and mechanical agitation such as, by mechanical brushing of the powder.
U.S. application Ser. No. 10/420,126, in which the present inventors are coinventors, is hereby expressly incorporated by reference. It discloses separation of superalloy metal powder from contaminants by enhancing the magnetic properties of the superalloy as by oxidizing or leaching of chromium at elevated temperature followed by magnetic separation of the contaminants from the superalloy metal powder. Mechanical agitation during heating is disclosed as a means for resisting agglomeration of the metal powder prior to magnetic separation.
In spite of the foregoing disclosures, there remains a very real and substantial need for reliable, safe, accurate and low-cost methods for producing aliquots from superalloy metal powder particles which are concentrated with respect to contaminants, such as process-produced contaminants, and which are amenable to microscopy analysis for statistically reliable quality assurance.
Overall as a result of the foregoing limitations, there exists a very real and substantial need for a reliable, safe, accurate and lower-cost method for producing aliquots from the superalloy metal powder particles which are concentrated with respect to contaminants, such as process-produced contaminants, and which are amenable to microscopy analysis for statistically reliable quality assurance.